Numerous boat trailers have been developed in the past with specific accommodations for receiving and distributing the weight of a boat between rollers or elongated "bunks" engaging the boat hull.
The keel area of a boat is typically designed to be relatively strong, while the hull areas are much more fragile. It is therefor desirable for the support devices in a boat trailer to engage the boat hull over a fairly large surface area to provide partial support and to support the remainder of the boat along the keel area.
It is undesirable to provide a large share of support along the keel, because the keel represents only a small fraction of the total surface area for potential support. Vibration and shock are concentrated in a much more confined area along the keel of a boat during transport and consequent damage is more prevalent when support is predominantly concentrated in the keel area. An "ideal" support will proportion the received weight of the boat in a desired relationship between keel supports and hull supports.
An attempt to provide improved support is disclosed in U.S. Pat. No. 3,512,667. The boat trailer in this patent includes self-centering or self-balancing cradle assemblies for hull engagement. Each cradle assembly is pivoted to the trailer framework about a transverse axis intermediate front and rear rollers that engage and carry a portion of the boat hull. Weight of the boat is balanced between the rollers on each cradle assembly. Two or more cradle assemblies are required to support a boat of any substantial size.
U.S. Pat. No. 3,785,677 discloses a weight distribution arrangement for boat trailers using single and multiple "walking beam" supports. The objective of this arrangement is to permit automatic self balancing through the hull supports during road travel.
The load support issue is also addressed in U.S. Pat. No. 3,993,324 with particular emphasis to supports using elongated flexible "bunks" for the purpose of supporting curved boat hulls, such as those on sailboats. This patent discloses a combination of longitudinal bunk support members, and walking beam supports. The bunks are mounted at rearward ends to the walking beam arrangement and at front ends to relatively fixed forward supports. The bunks are capable of pivotal motion about axes that extend substantially longitudinally with respect to the frame. The fixed nature of the forward mounts, however, limit the adaptability of the bunk support arrangement to various hull configurations.
Numerous other forms of trailer supporting apparatus have been provided in the past. Yet problems are still realized in the ability of the various trailers to adapt to numerous hull configurations for various boat styles and to apportion support between the hull and keel areas.
It is typical for adjustments to be made to the various hull engaging arrangements to adapt individual trailer configurations to a particular hull shape. Yet this adjustment often has an adverse effect on load distribution between the keel and hull supports on the trailer frame. Some trailers provide load distribution adjustment capability but do not adapt easily to different hull configurations. A need has therefore remained for a boat hull support arrangement that will automatically adapt to individual hull configurations while maintaining a desired weight support ratio between the hull and keel engaging members thereof.